The Seikan Tunnel ('函トンネル Seikan Tonneru or '函隧" Seikan Zuidō) is a 53.85 km (33.49 mile) railway tunnel in Japan, with a 23.3 km (14.5 mile) portion under the seabed. It travels beneath the Tsugaru Strait " connecting Aomori Prefecture on the Japanese island of Honshu and the island of Hokkaido " as part of the Japan RailwaysKaikyo Line. Although it is currently the longest railway tunnel in the world (until the Swiss Gotthard Base Tunnel is completed), faster and cheaper air travel has left the Seikan Tunnel comparatively underutilized.
Japan Railway Construction Public Corporation established
September 28, 1971
Main tunnel construction commenced
January 27, 1983
Pilot tunnel holed through
March 10, 1985
Main tunnel holed through
March 13, 1988
Tunnel opened
Source:
Connecting the islands of Honshu and Hokkaido by a land route had been considered since the Taishō period (1912-1925), but serious survey only commenced in 1946, due to the loss of overseas territory at the end of World War II and the need to accommodate returnees. In 1954 five ferries, including the Toya Maru, sank in the Tsugaru Straight during a typhoon, killing 1430 passengers. The following year the Japanese National Railways (JNR) expedited the tunnel investigation.
Also of concern was the increasing traffic between the two islands. A booming economy saw traffic levels on the JNR operated Seikan Ferry double to 4,040,000 persons/year from 1955 to 1965, and cargo levels rose 1.7 times to 6,240,000 tonnes/year. In 1971, traffic forecasts predicted increasing growth that would outstrip the ability of the ferry pier facility, that was constrained by geographical conditions. In September 1971 the decision was made to commence work on the tunnel. A Shinkansen capable cross section was selected, with plans to extend the Shinkansen network.
Arduous construction in difficult geological conditions proceeded. 34 workers were killed during construction.
Tsugaru Strait traffic data
Year
Passengers (persons/yr)
Freight (T/yr)
Mode
1955
2 020 000
3 700 000
Seikan Ferry
1965
4 040 000
6 240 000
Seikan Ferry
1970
9 360 000
8 470 000
Seikan Ferry
1985
9 000 000 †'
17 000 000
1971 Forecast''
1988
~3 100 000
"
Seikan Tunnel
1999
~1 700 000
"
Seikan Tunnel
2001
"
>5 000 000
Seikan Tunnel
† This may be a typographical error in the source
On January 27, 1983 Japanese Prime Minister Yasuhiro Nakasone pressed a switch that set off a blast that completed the pilot tunnel. Similarly on March 10, 1985 Minister of Transport Tokuo Yamashita symbolically holed through the main tunnel.
However the project's success was questioned. The 1971 traffic predictions were overestimates. Instead of the traffic rate increasing to 1985, it peaked 1978 and then proceeded to decrease " attributed to the slowdown in Japan's economy since the first oil crisis in 1973 and to advances made in air-transport facilities and longer-range sea transport.
The tunnel was opened in 13 March1988, at a cost of 538.4 billion yen (US$3.6 billon).
Once the tunnel was completed all railway transport between Honshu and Hokkaido utilised the tunnel. However, for passenger transport 90% of people use air; due to speed and cost. For example to travel between Tokyo and Sapporo by train takes more than 10 hours and 30 minutes, with several transfers. By air the journey is 3 hours and 30 minutes, including airport access times. Also, deregulation and competition in domestic air travel has brought down prices on the Tokyo-Sapporo route, making rail more expensive.
Surveying started in 1946. In 1971, 25 years later, construction began. In August 1982 less than 700 m remained to be excavated. First contact between the two sides was in 1983.
The Tsugaru Strait has eastern and western necks, both approximately 20 km across. Initial surveys undertaken in 1946 indicated that the eastern neck was up to 200 m deep with volcanic geology. The western neck had a maximum depth of 140 m and geology consisting mostly of sedimentary rocks of the Neogene period. The western neck was selected, with its conditions considered favourable for tunnelling.
Geology of the undersea portion of the tunnel consists of volcanic rock, pyroclastic rock, and sedimentary rock of the late Tertiary era. The area is folded into a nearly vertical anticline, which meant that the youngest rock is in the centre of the Strait, and encountered last. Divided roughly into thirds: the Honshu side consists of volcanic rocks (ansesite, basalt etc); the Hokkaido side consists of sedimentary rocks (Tertiary periodtuff, mudstone, etc); and the centre portions consists of Kuromatsunaistrata (Tertiary period sand-like mudstone). Igneous intrusions and faults caused crushing of the rock and complicated the tunnelling procedures.
Initial geological investigation occurred from 1946 to 1963, and involved drilling the sea-bed, sonic surveys, submarine boring, observations using a mini-submarine, seismic and magnetic surveys. However, to establish a greater understanding, horizontal pilot boring was undertaken - in both the service and pilot tunnels.
Tunnelling occurred simultaneously from both the northern and southern ends. The dry land portions were tackled with traditional mountain tunnelling techniques, with a single main tunnel. However, for the 23.3 km undersea portion three bores were excavated with increasing diameters respectively: an initial pilot tunnel, a service tunnel and finally the main tunnel. The service tunnel was periodically connected to the main tunnel with a series of connecting shafts, at 600 - 1000 m intervals. The pilot tunnel served as the service tunnel for the 5 km centre portion.
Beneath the Tsugaru Strait use of a tunnel boring machine (TBM) was abandoned after less than 2 km due to the variable nature of the rock and difficulty in accessing the face for advanced grouting. Blasting with dynamite and mechanical picking were the excavation methods.
A 2002 report by Michitsugu Ikuma described, for the undersea section, that "the tunnel structure appears to remain in a good condition". The amount of inflow has been decreasing with time, although it "increases right after a large earthquake".
Each of the twin tracks inside the tunnel is built allowing for three rails, so that both narrow-gauge and standard-gauge trains can be handled. Currently, only narrow-gauge trains use the tunnel, but the Hokkaido Shinkansen project (which started construction in 2005) includes laying dual-gauge track and linking the tunnel into the Shinkansen network, so Shinkansen trains can traverse the tunnel to Hakodate (scheduled for 2015) and eventually Sapporo. Note that despite what some "official" references state, only narrow gauge track is currently laid through the tunnel. The tunnel has 52 km of continuous welded rail.
Two stations are located within the tunnel: Tappi-Kaitei Station and Yoshioka-Kaitei Station. The stations serve as emergency escape points. In the event of fire or other disaster the stations provide equivalent safety of a much shorter tunnel. The effectiveness of the escape shafts located at the emergency stations is enhanced by exhaust fans to suck up smoke, television cameras to route passengers to safety, thermal (infrared) fire alarm systems and water spray nozzles. Previously, both the stations contained museums detailing the history and function of the tunnel, and could be visited on special sightseeing tours. Now only Tappi-Kaitei remains as a museum, Yoshioka-Kaitei was demolished on March 16, 2006 to make way for Hokkaido Shinkansen preparations.
The name '函 (Seikan) is a contraction of the principal cities on the line through the tunnel. The first kanji is from '森 (Aomori) and the other from 函館 (Hakodate).
